GASEOUS SULFUR DIOXIDE ABSORPTION SYSTEM

1285934 Treating gases with liquids BABCOCK & WILCOX CO 4 Dec 1969 [10 Dec 1968] 59367/69 Heading B1R [Also in Division C1] In a process for absorption of SO, from a flue gas using an aqueous Mg(HSO 3 ) 2 -MgSO 3 absorbent, the gas is contacted with the atomised absorbent solution in a plurality of absorption zones, gas and liquid from each zone are separated, the major part of the liquid being recycled to the zone while the remainder is passed to the next zone in countercurrent to the gas flow, liquid is withdrawn from the first zone (in the direction of gas flow), and a compensating amount of makeup water is added to the system, being distributed between the zones in such a way as to maximise the efficiency of the absorption in the system and in particular, that in the last zone. Magnesium hydroxide slurry is also added to each zone at such a rate as to maintain the highest possible concentration of MgSO 3 without causing precipitation. The invention is illustrated by reference to treatment of flue gas containing 1% by volume of SO 2 from incineration of waste liquors in a pulp process to give a liquid in the first zone containing 4% SO 2 , which is returned to the process as cooking liquor. In each of three absorption zones 12, 27 and 36 the gas is contacted in a venturi scrubber 18, 30, 38 with the atomised absorbent. Gas and liquid are separated in the gas turning spaces 21, 31, 40 and the gas passes to the next zone by ducts 26, 32 while the liquid is partly recycled by lines 17, 35, 44 and partly passed to the preceding zones by lines 45, 46 or withdrawn by line 29. Magnesium hydroxide slurry is added through lines 53, 54, 55 and makeup water through lines 48, 50, 51. The best results are obtained by adding about 40-55% of the water to zone 36 and the remainder to zone 27.